Weather Observations Terminology

This page will help with interpreting surface observations like the following example report:
Station Sky Wx MSLP Temp Wind Peak
Juneau Airport OVC025 R-F 1031.5 36 0912G22 35

Sky

 The sky condition describes the predominant/average sky condition based on eighths of the sky covered by opaque (not transparent) clouds. The sky condition is encoded as a six character string SSSXXX where SSS is the sky condition and XXX is the height (in hundreds of feet) of the cloud layer.

From our example Juneau Airport observation: OVC025 = 8/8 of the sky covered at 2500 feet.

Sky Condition Opaque Cloud Coverage
OVC 8/8
BKN 5/8 to 7/8
SCT 3/8 to 4/8
FEW 1/8 to 2/8
CLR 0/8

Wx - Weather

The weather at the time of the observation is encoded as a variable length string of one-character weather types.
Precipitation types can be followed by an intensity modifier. The modifier can be either a "-" for light (Up to 0.10 inches/hr) precipitation, no modifier for moderate (0.11-0.30 inches/hr) precipitation, or "+" for heavy precipitation (more than 0.30 inches/hr).

Common Weather Types
R - Rain S - Snow W - Shower
L - Drizzle F - Fog T - Thunder
K - Smoke H - Haze D - Dust/Sand
Z - Freezing A - Hail I - Sleet
P - Precipitation, Unknown Type

MSLP

MSLP is the abbreviation for mean sea level pressure. It is normally reported in millibars where 1000 MB = 29.53 inches of mercury. Sea level pressure means the actual station pressure has been mathematically calculated to a value at a reference height of mean sea level. This allows more accurate comparison between stations at different elevations. Station pressure is also often used to determine the altimeter setting, used to indicate the height of an aircraft above a known reference surface.

Temp

The air temperature at the time of observation, indicated by a thermometer exposed to the air in a place sheltered from direct solar radiation.

Wind

The wind describes the prevailing direction from which the wind is blowing, with speeds in knots. The wind is encoded as DDFF where DD is the direction the wind is blowing from in tens of degrees and FF is the speed in knots. For speeds over 100 knots the wind would be encoded as DDFFF. A wind gust can also be included by appending the letter G to the prevailing speed, followed by the speed of the gust. Gusts are reported when the peak wind speed reaches at least 16 knots and the variation in wind speed between the peaks and lulls is at least 9 knots. The duration of a gust is usually less than 20 seconds. Peak wind represents the maximum instantaneous wind speed since the last observation that exceeded 25 knots.

From our example Juneau Airport observation: 0912G22 would mean a wind blowing from the east (90 degrees on the compass) at 12 knots with a gust to 22 knots and a peak wind of 35 knots.